1997 90hp Yam - fine for 10 minutes then runs ratty

[kevin475]

Thanks in advance for reading..

Here's the background. 1997 90HP Yamaha outboard. Launched it this year, put new fuel filter on, ran fine. Ten minutes into driving it to my slip it quit making full power. I limped a 3,000 rpm to my slip. Seemed like a fuel issue.

I get a new filter, drain the old into an empty water bottle and find the fuel looking like iced tea with a significant amount of water. I put a new filter on. Runs fine for 10 minutes then quits revving again. I drain the fuel filter again but this time looks ok with no water. I decide to have the tank drained. I install a new filter, new plugs and throw in a can of water zorb in case any remnent water contaminated fuel exists.

I take it out and runs fine for 10 minutes with the same issue. I have checked heat, compression, water flow thru the engine. All seem fine.

The thing runs up to 4,900 which has been typical and when it starts running bad it cuts back slowly until it wont make enough power to plane the boat. It never stalls/stops. I have an idea of what is the issue but I'm no oatboard mechanic. I was a decent jetski wrench back in my youth.

Thanks greatly for any insite.

Kevin

 

[robert graham]

Re: 1997 90hp Yam - fine for 10 minutes then runs ratty

Remove black plastic airbox from front of motor(4 phillips head screws), drain each carb(10mm brass hex screw at bottom side of each carb) onto a clean white rag to see if you have water or trash in carbs. With drain screws out pump primer bulb to flush each carb float chamber with fresh gas, replace drain screws. This may help your problem and give you an idea if carbs are fouled and need cleaning. Good luck and let us know what you find.

 

[kevin475]

Re: 1997 90hp Yam - fine for 10 minutes then runs ratty

Thanks for the reply Robert.

The fuel in the carbs seemed clean. I also cleaned the plastic fuel filter located behind the oil tank.

I went to test drive it and this time it ran ratty right out of the gate. It starts and idles perfectly. It just won't rev.

I'm still leaning towards dirty carbs but............

Any other suggestions?

 

[robert graham]

Re: 1997 90hp Yam - fine for 10 minutes then runs ratty

Carb jets probably plugged and need cleaning, but be sure entire fuel system is flushed and clean or they'll plug back up quickly after cleaning. Probably good that it's running poorly because you probably have a lean fuel condition and not good for pistons, etc. Good Luck and let us know what you find.

 

[kevin475]

Re: 1997 90hp Yam - fine for 10 minutes then runs ratty

Thanks Robert,

Had a mechanic come out and clean the carbs. Debris was the culprit. Life is good and boat runs well.

Thanks again.